electrical current running through my Tibook

When i plug in tibook incorrectly there is an electrical current that runs through it. I can feel it when i run my hand over the case. I figured out that it only happens when I plug the computer in backwards. Let me explain, both ends of the power plug prongs fit into the small electrical slot. That means that I am never sure when pluging it in if I am doing it correctly or the wrong way. The only way to tell is to run my hand over the case and see if I can feel an electrical charge. I was just wondering if I should contact apple about the problem? is there a chance that this could damage my tibook?